The present invention relates to adhesives, and particularly adhesives for connecting a semiconductor chip to a wiring board.
Adhesives based on a thermosetting or thermoplastic resin have been used to bond a semiconductor element onto a wiring board.
FIG. 4 shows that a semiconductor chip 111 is applied on a wiring board 113 via an adhesive 112, and bump-like terminals 121 on the semiconductor chip 111 are in contact with terminals 122 formed of parts of the wiring pattern on the wiring board 113. In this state, electric components in the semiconductor chip 111 are electrically connected to the wiring pattern on the wiring board 113 via the terminals 121, 122.
However, the adhesive 112 has a linear expansion coefficient of 25-60 ppm/xc2x0 C., which is higher than that of the semiconductor chip of about 3 ppm/xc2x0 C., leading to residual stress at the bonding interface due to the difference of the linear expansion coefficient. Especially, the residual stress increases with the chip size at the periphery of the semiconductor chip, which causes the problem that semiconductor chip 111 may be separated during temperature cycle tests or pressure cooker tests after the thermosetting adhesive 112 is cured.
Moreover, adhesives of the prior art show a marked deterioration of reliability under some moisture adsorption conditions after the semiconductor chip 111 has been bonded, which required a dehydration process by preheating to about 100xc2x0 C. before the assembly is passed through a reflow furnace to cure the adhesive 112 after the semiconductor chip 111 is applied.
The present invention was made to overcome the disadvantages of the prior art described above with the purpose of providing a highly reliable adhesive.
The present invention provides an adhesive for connecting a semiconductor chip and a wiring board, comprising a first resin component which is polymerizable, a first hardener for inducing a self-polymerization reaction of the first resin component, and a second hardener which is addition-polymerized with the first resin component.
The present invention provides the adhesive having an elastic modulus decreasing with a temperature increase after curing, wherein the elastic modulus loss sharply increases at both of a first temperature higher than 30xc2x0 C. and lower than 150xc2x0 C. and a second temperature within a range of 130xc2x0 C. or more and 250xc2x0 C. or less and higher than the first temperature. The difference between the first temperature and the second temperature is preferably 40xc2x0 C. or more.
The present invention provide the adhesive wherein a ratio of an elastic modulus at the first temperature to an elastic modulus at the second temperature is 2.8 or more. The present invention provides the adhesive wherein the first resin component is an epoxy resin. The adhesive may also contain (1) conductive particles, (2) filler and/or (3) a second resin component which is polymerized separately from the first resin component.
The present invention further provides the adhesive wherein the first hardener is one or more of an imidazole, a tertiary amine or a Lewis acid catalyst and the second hardener is one or more of an active hydrogen-containing amine, a phenol, a hydrazide, a mercapto or a dicyandiamide hardener. The present invention provides the adhesive wherein the adhesive further contains a filler of silica, alumina or titanium oxide.
The adhesive may be preliminarily semicured and formed in the form of a sheet.
The present invention provide an electric device comprising a semiconductor chip and a wiring board, wherein the semiconductor chip is adhesively bonded to the wiring board with the adhesive.
The present invention provides the electric device wherein the semiconductor chip includes connection terminals that contact connection terminals of a wiring pattern on the wiring board.